ntermittent fasting is the eating pattern that celebrities like Jennifer Aniston, Elle Macpherson and Reese Witherspoon consistently check as part of their wellness routine.
There are a number of different approaches to intermittent fasting, which basically involves alternating between cycles of eating and fasting. They include periodic fasting, alternate-day fasting and time-restricted eating, the latter of which is gaining particular attention at the moment, with a number of new iterations of the method having been recently released.
While some dismiss intermittent fasting as a “fad diet” – and let’s be clear, it certainly won’t suit everyone – some health experts argue that we were not built to be constantly digesting food and that if paired with a healthy, balanced diet and active lifestyle, giving yourself periodic breaks can be an effective way of maintaining a healthy weight (without having to cut out food groups or count calories at meals). Some proponents also claim it leaves them feeling more energised and with better concentration levels.
Here are all of your questions about intermittent fasting answered by nutritional experts.
What are the most popular methods of intermittent fasting ?
Dr Michael Mosley is largely credited for taking intermittent fasting into the mainstream when he developed the 5:2 diet. He has since updated his guidelines for this plan to become the Fast 800 – it involves eating normally for five days of the week and restricting your calorie intake to a measly 800 for the remaining two (it used to be 500 calories). He also recommends time restricted eating and following a Mediterranean diet alongside the plan, read our interview with him here on why.
If you don’t want to count calories – who does these days? – time-restricted eating plans like the 16:8 offer an alternative form of intermittent fasting – and is the chosen plan of the aforementioned celebs. Harley Street nutritional therapist Olga Hamilton also follows the method, which involves a 16-hour fasting period followed by and eight-hour window in which to eat all of your meals. “I start my feeding window at 1pm with a large lunch and finish eating my dinner by 9pm at the latest.”
Isn’t it unhealthy to skip breakfast? This is a hotly contested subject in the health and wellness world and there are studies to support both sides of the argument. Some say it’s a myth, and that the problem is that those who typically skip breakfast have unhealthy lifestyles. “Eating breakfast doesn’t kickstart our metabolism and skipping it won’t make you overeat during the day,” Smith argues. “The first meal of the day is your breaking fast – hence ‘break-fast’ – so just focus on keeping this meal healthy.”
In reality, we’re all different and our bodies and circadian rhythms all react differently to eating times and patterns.
There are a growing number of other health experts who argue it’s not so much what you eat but when you eat. In his recently released title Feel Great Lose Weight, Dr Rangan Chatterjee, who has over two decades of experience as a GP, suggests a 12-hour eating window may be the key to maintaining a healthy weight. Meanwhile in nutritionist Jeannette Hyde’s upcoming The 10 Hour Diet, she argues that by simply fitting all of your eating and drinking into 10 hours, you can give yourself a complete health overhaul.
How does intermittent fasting work?
A 2019 study found time-restricted eating may aid weight loss by reducing your appetite, so that you end up consuming less over the course of the day. Equally, it’s important to point out, that other studies have found that periodic fasting, when you restrict your calorie intake on a couple of days a week, may cause some people to overeat on non-fasting days.
The theory is that fasting alters the way the body stores energy, Smith says. “When we eat, some of the energy we get from food is immediately available whilst some is stored for future use. Our insulin levels also increase and excess glucose is stored in the liver, but often the liver has no storage space so it is converted into fat. When we fast, this process is reversed. Insulin and blood levels fall, signalling to the body to burn stored energy.”
What are the potential health benefits of intermittent fasting?
Some studies have shown that intermittent fasting may help with weight loss; improve blood sugar control; insulin sensitivity; lower your risk of type 2 diabetes; promote cellular renewal; increase blood levels of growth hormone; encourage fat burning and muscle growth and improve cognitive function. This is on top of just generally giving the body a break from all of the processing it does.
Does fasting affect your mental health? Fasting has been shown to increase rates of neurogenesis in the brain, Hamilton says, encouraging the growth and development of new brain cells and nerve tissues. “Fasting also boosts production of BDNF protein that has been found to play a significant role in neuroplasticity, which in turn can make your brain more resilient to stress, boost memory and even improve mood,” she adds.
It is, however, crucial to point out that as intermittent fasting is still a relatively new phenomena, the long-term effects are still unknown.
How long does it take to feel the benefits?
Some people report side effects such as hunger pangs, headaches, crankiness and feeling physically and mentally weak, particularly when they first start following an intermittent diet, so it’s crucial to ease your way in.
How fast you see results depends on what you eat and your levels of physical activity. “Intermittent fasting is more effective when combined with a healthy diet and lifestyle, i.e. high-quality nutrient rich food consumption and some form of regular exercise or movement,” Smith says. “It is perhaps the fastest and most effective way to achieve weight loss. I do it for clarity of mind, productivity, focus and optimal digestive function.”
Can you drink while fasting?
It’s important you drink fluids during fasting periods. “Choose non-calorific clear fluids, ideally water and herbal tea,” advises Smith. “Tea and coffee is allowed, but should ideally be black. If you add milk, 1-2 teaspoons is OK, but no sweeteners or sugar, of course. Avoid alcohol, energy drinks and drinks that claim to be sugar free.”
Most intermittent fasting plans don’t require you to completely cut out alcohol (just during your fasting window, and in moderation of course!) which is another attraction of the diet for some.
Who should avoid intermittent fasting?
Intermittent fasting is not going to suit everyone and nutritionists advise that it should be avoided by anyone with a history of eating disorders, who is malnourished or on medication, children and teenagers, pregnant and breastfeeding women.